Hydraulic vehicle drive and valve module for same

ABSTRACT

A hydraulic vehicle drive, particularly for mobile hoisting platforms, has a first pair of wheels drivable by means of first wheel motors ( 8, 9 ) in dependence of a first control valve ( 2 ) and a second pair of wheels provided with second hydraulic motors ( 15, 16 ). A switching arrangement ( 19 ) short-circuits the second hydraulic motors ( 15, 16 ) in the driving-free state and for cooling supplies them with a flushing flow. In the driven state a second control valve ( 5 ), in dependence of which the second hydraulic motors ( 15, 16 ) are drivable, is activated, and if required connected with the first control valve ( 2 ). Thus, optionally, the first wheel pair can be driven alone or together with a certain driving output from the second wheel pair.

[0001] The invention concerns a hydraulic vehicle drive, particularlyfor mobile hoisting platforms, with a first pair of wheels drivable bymeans of first hydraulic motors in dependence of a first control valve.

[0002] Numerous vehicles are available in the market, with either two orfour hydraulically driven wheels. The two-wheel drive is suited forsimple ground with only small slopes and particularly for indoor use.The four-wheel drive is required for difficult ground with larger slopesor for building sites. Until now the application fields have beenlimited by the type of driving.

[0003] Valve modules with constant flow quantity (flow control) and withconstant outlet pressure (pressure control) are known from DE 38 02 672C2, which valve modules have substantially the same design and onlydiffer in a few details. In these valve modules, a compensation valveand a control valve enabling the driving of a motor in both directionsare connected in series.

[0004] It is the purpose of the invention to provide a hydraulic vehicledrive of the kind described in the introduction, which permits theoptional driving of one pair of wheels, for example the two frontwheels, or two pairs of wheels, for example the front and the rearwheels.

[0005] According to the invention, this task is solved by means of asecond pair of wheels provided with second hydraulic motors and with aswitching arrangement, which short-circuits the second hydraulic motorsin the driving-free state and, for the purpose of cooling, supplies themwith a flushing flow, and in the driven state activates a second controlvalve in dependence of which the second hydraulic motors are drivable.

[0006] By means of the switching arrangement, one pair of wheels can bedriven or a second pair of wheels can be connected optionally. In theresting state of the switching arrangement it is provided that thewheels of the second pair can turn freely and that a too strong heatdevelopment is prevented. In the connected state the second wheel pairalso works, and for this purpose it can, like the first wheel pair, becontrolled by, for example, a user.

[0007] Preferably, the switching arrangement connects the second controlvalve with the first control valve. This connection of the two controlvalves makes the driving of the second wheel pair adapt to that of thefirst wheel pair. The connection can be mechanical or hydraulic,however, preferably electrical, for example also in the form of a remotecontrol.

[0008] Particularly advantageous is that the degree of connectionbetween the first and the second control valve is adjustable. Thus, theuser can select the contribution of the second motors to the drivingoutput, if required even dynamically, that is adjustable duringoperation. The driving output can, for example, be adjusted between 0and 100% of the output, which the second hydraulic motors would supplyat a certain driving output of the first hydraulic motor. At the sametime, a very simple steering can be achieved via the connection.

[0009] It is favourable that the fist control valve is a first valvemodule with constant flow quantity. Thus, the first wheel pair is drivenwith a flow quantity, and thus also a speed, which depends on theposition of the first control valve.

[0010] Further, it is expedient that the second control valve is asecond valve module with constant outlet pressure. In the case of adynamic connection, for example the outlet pressure can be set. When inthe connected state the second valve module is active, the second wheelpair does not only receive the required flow quantity, but a pressurefor creation of a sufficient torque is maintained. The use of valvemodules is also an advantage, because the usually available moduleblock, which is provided for all functions (direction control, hoistingand lowering functions, front-wheel drive), merely has to besupplemented by the second valve module required for the four-wheeldrive.

[0011] Advantageously, it is provided that the main slide of the firstcontrol valve is adjustable by means of an operating element and that inthe driven state the main slide of the second control valve isadjustable proportional to the main slide of the first control valve.This is a particularly simple way of connecting the two control valves.With a rigid connection the proportionality factor can be fixed and witha dynamic connection the proportionality factor can be adjustable.

[0012] Further, it is advantageous that a lever serves as operatingelement, which lever is pivotal for the adjustment of the first controlvalve and has a trigger for the operation of the switching arrangement.This gives a very simple handling of the driving arrangement. Thetrigger can also be used for setting the size of the share of thedriving output from the second hydraulic motor, that is, for example,the adjustment of the proportionality factors.

[0013] It is also recommended that the switching arrangement has acontrol valve connecting the two sides of the second hydraulic motorswith each other in the driving-free state, however separating them inthe driven state. This control valve enables the requiredshort-circuiting of the hydraulic motors in the resting state.

[0014] Further, it is advantageous that the second hydraulic motors havea leakage channel and that in the driving-free state of the switchingarrangement they are connected with a pump connection via a pressuredependent valve arrangement. Using the leakage channel offers a simpleway of realising the flushing flow.

[0015] It is a substantial advantage that the second valve module has acompensation valve and a main slide, which has two annular slide slotswith axial slots originating from those, and which is arranged in a borewith a central annular pump slot, annular motor slots arranged on bothsides of said pump slot, as well as annular tank slots arranged outsidesaid motor slots, the central axial slots having such a length that inthe neutral position of the main slide they connect the annular motorslots with the annular pump slot, however separating one of theseconnections during a displacement. A minor extension of the centralaxial slot in a valve module for constant outlet pressure causes thatthe annular motor slots are connected with each other, which leads tothe desired short-circuiting of the second hydraulic motors,additionally permitting a certain flushing flow through the secondhydraulic motors in connection with the compensation valve.

[0016] Additionally, protection is claimed for a valve module asseparate commercial unit, which is characterised by a housing with apump connection, two motor connections and a tank connection as well asa main slide bore having a central annular pump slot connected with thepump connection via a compensation valve, two annular motor slotsconnected with motor connections being arranged on both sides of saidpump slot, and two annular tank slots connected with the tank connectionand arranged outside said motor slots, and by a main slide having twoannular slide slots with axial slots originating from those, of whichthe two central axial slots have such a length that in the neutralposition of the main slide they connect the annular motor slots with theannular pump slot, however separating one of these connections during adisplacement.

[0017] In the following the invention is described on the basis ofpreferred embodiments in connection with the drawings, showing:

[0018]FIG. 1 a circuit diagram of a vehicle drive according to theinvention

[0019]FIG. 2 a section through a valve module applicable according tothe invention

[0020]FIG. 3 the circuit diagram of this valve module

[0021]FIG. 4 the circuit diagram for a valve module suited for thetwo-wheel drive

[0022] The circuit diagram in FIG. 1 shows a valve block 1 with fourvalve modules 2, 3, 4 and 5. The valve block 1 is supplied with pressurefluid by a pump 6, which is connected with a pump connection P. In theusual way the pump 6 can be driven by an electric motor or a combustionengine. A tank connection T is connected with a tank 7. All valvemodules have two motor connections A and B.

[0023] A valve module serves as control valve 2 for hydraulic motors 8and 9, which drive two front wheels. For this purpose the motorconnections A and B are connected with motor hoses 10 and 11 via pilotcontrolled non-return valves 12. They ensure that on an inclined surfacethe vehicle will remain braked. Due to the inner leakages, it will bepractically impossible to reach a complete blocking. Accordingly, anadditional mechanical brake will often be provided. The valve modulecomprises a proportional valve which keeps the set flow quantityconstant. The setting is made by means of an operating element 13, hereshown as a joystick, which is pivoted in the direction of the arrow 14.

[0024] A subsequent valve module serves as control valve 3 for thedirection steering, which can, for example, be operated by means of apivoting movement of the operating element 13 transversal to thedirection of the arrow 14. The steering motor required in connectionwith this is not shown.

[0025] A third valve module serves as control valve 4 for an additionalsteering function, here the hoisting and lowering function of a hoistingplatform. This steering can, for example, be triggered by means of asecond operating element, which is not shown, as is not the requiredhoisting motor.

[0026] A fourth valve modules serves as control valve 5 for twohydraulic motors 15 and 16, which drive two rear wheels. For thispurpose the motor connections A and B are connected with the motor hoses17 and 18. The operation occurs in synchronism with the steering module2. The control valve 5 is dimensioned for constant output pressure.

[0027] In stead of two hydraulic motors per axle, only one motor can beprovided.

[0028] With regard to the design of such control valves, DE 38 02 672 C2is referred to, in which the FIGS. 1 to 3 and 7 show a control valvewith constant flow quantity and the FIGS. 4 to 6 and 8 show a controlvalve with constant output pressure.

[0029] According to the invention, the hydraulic motors 15 and 16 areonly intended for optional driving. For this reason a switching device19 is provided, which is operable by means of a trigger 20, which can beactivated in the direction of the arrow 21. In the non-activated statethe control valve 5 remains in the neutral position, so that thehydraulic motors 15 and 16 are not driven. In order that the rotors ofthe motors 15 and 16 can rotate freely, a control valve 22 is provided,which short-circuits the motor hoses 17 and 18. An additional valvearrangement 23 has a control valve 24, a pressure dependent valve 25 andtwo non-return valves 26 and 27. Via this valve arrangement the twohydraulic motors 15 and 16 receive a small quantity of pump fluid, whichcan flow off again via the leakage channels 28 and 29 of the hydraulicmotors 15 and 16. In this way a cooling is obtained.

[0030] The control valves 22, 24 can, for example, be solenoid valves.Depending on the steering, they are open or closed in the de-energisedstate.

[0031] When the trigger 21 is operated, the control valve 5 isfunctionally connected with the control valve 2, so that they areadjusted proportionally to each other. At the same time the controlvalves 22 and 24 are brought to their closed position, so that thebalancing function and the cooling function are abolished.

[0032] The trigger 21 can also be used to set the degree of theconnection, that is, the proportionality factor, between the two controlvalves 2, 5. When, for example, the trigger 21 is pushed further in, theshare of the second hydraulic motors 15, 16 to the total driving outputincreases.

[0033] In a third alternative the trigger 21 can also be used for directcontrol of the hydraulic motors 15, 16. In this case the operatingelement 13 is, for example, pushed in the direction of the arrow 14, tostart driving. If an additional driving output should be required, thetrigger 21, which is then made as a proportional element, can be pushed.The more the trigger 21 is pushed, the larger is the torque contributionof the hydraulic motors 15, 16. A connection of the control valves 2,5is then not absolutely necessary.

[0034] The operating element 13 can also have any other form known inpractice, for example a foot pedal. For example, the operating element13 can be connected with regulating units of the control valves 2 to 5via electrical cables or wirelessly. This remote control is particularlyinteresting, when the operator stands on a hoisting platform and wantsto move this platform to new positions both horizontally and vertically.

[0035]FIG. 2 shows a valve module 105 supplying a constant outputpressure and also comprising the functions of control valve 22 and valvearrangement 23. A housing has a pump connection P, two motor connectionsA and B and a not shown tank connection T. A main slide bore has acentral annular pump slot 33 connected with the pump connection P via acompensation valve 32, two annular motor slots 34 and 35 arranged onboth sides of the annular pump slot and connected with the motorconnections A and B, and two annular tank slots 36 and 37 arrangedoutside the annular motor slots and connected with the tank connectionT. A main slide 38 adjustable in the main slide bore 31 by means of notshown regulating units, for example electromagnets, has two annularslide slots 39 and 40. Two central axial slots 41 and 42 and two outeraxial slots 43 and 44 originate from these slide slots. These axialslots are made as flat indentations with decreasing depth towards theends. Further, load pressure sensor openings and channels are provided,which are shown in the circuit diagram in FIG. 3 by means of dottedlines LS and described in detail in DE 38 02 672 C2.

[0036] A difference in relation to the control valve with constantoutput pressure known from the patent document mentioned is in this casethat the central axial slots 41, 42 have such a length that in theneutral position of the main slide 38 they connect the two annular motorslots 34 and 35 with the annular pump slot 33. Thus the two motorconnections A and B and also the two motor hoses 17 and 18 areshort-circuited in the neutral position. Further, a small quantity ofpump fluid is supplied to the system by means of the compensation valve32, which flows on via the motor connection carrying the lowest pressureto the two hydraulic motors 15 and 16, from where it can be drained offvia the leakage channels 28 and 29. If, however, by operating thetrigger 20 the main slide 38 is brought to a working position, thecontrol valve 105 works as a normal control valve with constant outputpressure.

[0037] Of course, more axial slots than the two shown, 41 and 42, can beprovided. Also their shape can be different from the one shown. Theshape and the number can, for example, be selected in dependence of themotor size, the maximum driving speed or similar influencing sizes.

[0038] Finally, FIG. 4 shows the circuit diagram of the control valve 2,which permits the setting of a constant flow quantity. For furtherdetails, see DE 38 02 672 C2.

1. Hydraulic vehicle drive, particularly for mobile hoisting platforms,with a first pair of wheels drivable by means of first hydraulic motorsin dependence of a first control valve, characterised by a second pairof wheels being provided with second hydraulic motors (15, 16) and witha switching arrangement (19), which short-circuits the second hydraulicmotors (15, 16) in the driving-free state and, for the purpose ofcooling, supplies them with a flushing flow, and in the driven stateactivates a second control valve (5; 105) in dependence of which thesecond hydraulic motors (15, 16) are drivable.
 2. Vehicle driveaccording to claim 1 , characterised in that the switching arrangement(19) connects the second control valve (5; 105) with the first controlvalve (2).
 3. Vehicle drive according to claim 2 , characterised in thatthe degree of connection between the first and the second control valve(5; 105) is adjustable.
 4. Vehicle drive according to one of the claims1 to 3 , characterised in that the fist control valve (2) is a firstvalve module with constant flow quantity.
 5. Vehicle drive according toone of the claims 1 to 4 , characterised in that the second controlvalve (5) is a second valve module with constant outlet pressure. 6.Vehicle drive according to one of the claims 1 to 5 , characterised inthat the main slide (138) of the first control valve (2) is adjustableby means of an operating element (13) and that in the driven state themain slide (38) of the second control valve (5) is adjustableproportional to the main slide (138) of the first control valve (2). 7.Vehicle drive according to one of the claims 1 to 6 , characterised inthat a lever serves as operating element (13), which lever is pivotalfor the adjustment of the first control valve (2) and has a trigger (20)for the operation of the switching arrangement (19).
 8. Vehicle driveaccording to one of the claims 1 to 7 , characterised in that theswitching arrangement (19) has a control valve (22) connecting the twosides of the second hydraulic motors (15, 16) with each other in thedriving-free state, however separating them in the driven state. 9.Vehicle drive according to one of the claims 1 to 8 , characterised inthat the second hydraulic motors (15, 16) have a leakage channel (28,29) and that in the driving-free state of the switching arrangement (19)they are connected with a pump connection (P) via a pressure dependentvalve arrangement (23).
 10. Vehicle drive according to one of the claims5 to 9 , characterised in that the second valve module has acompensation valve (32) and a main slide (38), which has two annularslide slots (39, 40) with axial slots (41 to 44) originating from those,and which is arranged in a bore (31) with a central annular pump slot(33), annular motor slots (34,35) arranged on both sides of said pumpslot, as well as annular tank slots (36, 37) arranged outside said motorslots, the central axial slots (41, 42) having such a length that in theneutral position of the main slide (38) they connect the annular motorslots (34, 35) with the annular pump slot (33), however separating oneof these connections during a displacement.
 11. Valve module for ahydraulic vehicle drive according to one of the claims 1 to 10 ,characterised by a housing (30) with a pump connection (P), two motorconnections (A, B) and a tank connection (T) as well as a main slidebore (31) having a central annular pump slot (33) connected with thepump connection (P) via a compensation valve (32), two annular motorslots (34, 35) connected with motor connections (A, B) being arranged onboth sides of said pump slot, and two annular tank slots (36, 37)connected with the tank connection (T) and arranged outside said motorslots, and by a main slide (38) having two annular slide slots (39, 40)with axial slots (41 to 44) originating from those, of which the twocentral axial slots (41, 42) have such a length that in the neutralposition of the main slide (38) they connect the annular motor slots(34, 35) with the annular pump slot (33), however separating one ofthese connections during a displacement.